Self-cleaning oven with temperature limiting protection system

ABSTRACT

A self-cleaning oven having a single high limit thermostat which protects against an over-temperature condition inside the oven and a cooling fan failure outside the oven.

United States Patent l l3,619,564

[72] Inventor George W. Schlucl'Jr. [50] Field of Search 219/393,Dayton, Ohio 396, 398,412,413,511 [21] Appl. No. 56,485 221 Filed July20, 1970 References Cited [45] Patented NOV. 9, 1971 UNITED STATESPATENTS [731 '8" 3,327,094 6/1967 Martin et a1. 219/393 3,350,04210/1967 Getman 219/412 3,353,004 11/1967 Alexander.... 219/398 3,484,85812/1969 Jordan et a1. 219/413 [54] SELF-CLEANING OVEN WITH TEMPERATURELIMITING PROTECTION SYSTEM Primary Exammer-Volodymyr Y. Mayewsky 4Claims, 3 Damn: 8L Att0rneys-William S. Pettigrew and Frederick M.Ritchie [52] US. Cl 219/413, M

219/393, 219/398 ABSTRACT: A self-cleaning oven having a single highlimit [51] Int. Cl ..F27d 11/02, thermostat which protects against anover-temperature condi- "I Qsm tion inside the oven and a cooling fanfailure outside the oven.

SELF-CLEANING OVEN WITH TEMPERATURE LIMITING PROTECTION SYSTEM Prior artself-cleaning ovens provide temperature limiting protection whichoperate upon failure of the primary oven temperature control systems,e.g., either the cooling fan system or oven thermostat system. Suchprotection, e.g., is part of the self-cleaning oven model RBE-94Nmanufactured by Frigidaire Division of General Motors. This prior artoven includes both a fan safety thermostat and an oven safety thermostat.

The oven safety thermostat is a single pole, manual resettype switchwith a liquid-filled capillary line and bulb assembly. The capillaryline and bulb assembly are stainless steel. The bulb section is clampedto the oven liner at the top right corner. The switch is calibrated totoggle open at l,0l5 F. :l5 and remain open until the reset button ispushed to manually reset the switch.

The fan safety thermostat is a bimetal disc type. It is calibrated toopen during temperature rise at l85iX 6 F., and then reclose ontemperature decrease at l45:t9 F The thermostat and its disc portion isflush mounted to the insulation retainer panel behind the control panel.The thermostat is a safety device which opens the electrical circuit tothe thermal relay for the oven in the event an overtemperature situationoccurs, stopping the bake and broil elements from heating. The mostprobable cause of an open fan safety thermostat is an inoperative blowerfan.

This invention is directed to a temperature limiting protection systemwhich combines into one thermostat the protective functions of both thefan safety thermostat and the oven safety thermostat.

It is, therefore, a general object of my invention to provide asimplified and improved temperature protection system for aself-cleaning oven.

A more specific object of this invention is the provision of a singlethermostat positioned with respect to the air-cooling system and theoven heating system in a manner to sense failure of either system.

Another specific object of this invention is the provision of a singlethermostat for protecting against failure of the oven cooling system andthe oven heating system wherein the thermostat is positioned on aheat-sensing ferrule to sense excessive temperature in the oven vent andin exposed air-cooled relation to the exhaust air of the cooling systemto sense fan failure.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown. IN THE DRAWINGS FIG. I is a fragmentary side sectionalview of a self-cleaning oven provided with this invention;

HFIG. 2 is an exploded view of the temperature sensing components ofthis invention; and

FIG. 3 is a schematic wiring diagram illustrating the operation of thisinvention.

In accordance with this invention and with reference to FIG. I, abuilt-in wall oven I0 is illustrated. The wall oven includes a boxlikeoven liner 12 having a front opening 14 closed by an access door 16. Theoven liner 12 is surrounded by an inner oven cabinet or insulationretainer 18 and spaced therefrom by fiber glass insulation 20. An outeroven cabinet 22 surrounds the insulated oven liner and is spaced fromthe inner oven cabinet 18 to form a cooling air passageway 24. The airpassageway terminates at the front of the oven in a control panel 26which includes an air outlet grille overlying the oven access door 16.

A cooling air system is provided to envelop the insulated oven linerwith a cooling air flow. For this purpose the air passageway 24 includesa transverse partition 30 which divides the air passageway 24 into apositive pressure plenum chamber 32 and a negative pressure chamber 34.A blower means or motor-driven fan 36 is positioned in an opening of thetransverse partition 30 and is operable to pull cooling air around thesides of the insulated oven liner and up the back thereof to thenegative pressure chamber 34 from whence the cooling air is forced intothe plenum chamber 32 and out of the air outlet 28.

The self-cleaning oven includes a heating means within the oven linerfor heating the oven cavity 40. The heating means includes abroil-heating element 42 at the top of the oven liner and a bake-heatingelement 44 (not shown) at the bottom. An oven temperature controlassembly or oven thermostat means 46 is positioned on the control panel26 and operates to control the heating means for providing in the ovencavity either a cooking temperature between l50 and 550 F. or apyrolytic cleaning temperatures of about 900 F.

With reference to the schematic wiring diagram in FIG. 3, the oventemperature control assembly or oven thermostat 46 includes thoseelements included within the phantom line boxes. The assembly consistsof a Bakelite switching case and a helium gas-filled capillary, bulb andbourden tube (not shown). The assembly also has an internal cam tocorrelate the operation of three pairs of single pole, single throwcontacts 50, 52 and 54 and two pairs of single pole double throwcontacts 56, 58. One pair 52 of SPST contacts cycle open and closeddepending on oven temperature, opening and closing in response theretoan oven temperature responsive switch means 53 in series electricalsupply relationship with said heating means 42, 44. The switch 53 ispart of a thennal relay including a heater 55 and, of course, could beused to control a gasvalve where the power supply for the oven heatingmeans is gas. When contacts 52 are closed, the oven elements 42, 44 areheating; when opened, these elements are not heating. Another pair 50 ofSPST contacts are closed below an oven temperature of 560 F. and openedabove an oven temperature of 560 F. When this switch is opened, a locksolenoid 60 is inoperable so that the access door 16 cannot be openedduring a pyrolytic self-cleaning operation. The contacts 54'arccssentially line switch contacts to the heater 55 of the thermal relay.Whenever contacts 54 are opened (such as at OFF" setting), the thermalrelay heater 55 cannot be energized to close the relay contacts 53;whenever contacts 54 are closed (such as BAI(E" or BROIL settings), thethennal relay heater can be energized depending upon whether the cyclingcontacts 52 are closed. At CLEAN" setting, contacts 54 are open but thecircuit to the thermal relay heater 55 is provided through the SPSTinterlock switch 66 which is closed when the door is closed and locked.The remaining contacts in the oven temperature thermostat are the SPDTcontacts 56, 58 which circuit I18 volts or 236 volts to the heatingelements 42, 44 depending on whether the oven temperature thermo" statis set for BAKE," BROIL" or CLEAN."

The circuit may also include a door switch 70 in series with an ovenlamp 72 which is adapted to illuminate the oven cavity when the accessdoor 16 is opened. A look lamp 74, operating in conjunction with aresistor 75, is adapted to illuminate when, during an oven cleaningcycle, the oven temperature exceeds 560 F. and the switch 50 opens. Aconventional clock timer switch 76 is provided to time the oven cookingand cleaning operations. In this regard, an oven pilot light andcapacitor circuit 78 indicates the cycling of heating elements 42,44.

In the prior art, multiple devices were provided to protect againstovertemperature. In accordance with this invention, a singleovertemperature protective means 80 guards against excessive temperatureoccasioned either by a faulty oven temperature control assembly 46 or afailure of the cooling air fan 36.

The overtemperature protective means 80 includes a temperature limitingthermostatic switch means 82 and a cylindrical aluminum sensing ferrule84 for supporting the switch means. The switch means 82 is an exposeddisc bimetal type thermostat adapted for surface mounting. It iscalibrated to open at 243i6 F. and close at 203: F.

The sensing ferrule 84 is made of 0.032 aluminum and has a diameter of0.88 inches across its upper annular flange 86, a

diameter of 0.562 inches across its depending collar 88 and a height of0.42 inches. The inner oven cabinet 18 has an opening 90 sized toreceive the collar portion $8 of the sensing ferrule and the exposedbimetal disc portion 89 of the thermostatic switch means 82 is adaptedto nest within the flange 86 of the ferrule, thereby closing the openupper end of the ferrule.

The oven cavity 40 is provided with a vent opening in the top wall ofthe oven liner at 92. A flow-through catalyst package 94 is positionedwithin the vent opening. it is housed on the outside of the oven liner12 in a catalyst housing 96 which forms one part of a duct means placingthe oven cavity 40 in communication with the atmosphere through thecatalyst package 94. The other portion of the duct means is an oven vent98 leading to an oven casing opening 105) in communication with theatmosphere between the access door 16 and the exhaust outlet opening 28.The catalyst package 94 is of a type presently sold by the FrigidaireDivision of General Motors Corporation for the use in the exhaust outletof its current self-cleaning ovens. The catalyst package is filled witha bead-type catalyst more fully described in copending application Ser.No. 835,678 assigned to the same assignee as this application.

The housing for the thermostatic switch 82 is placed in the airstream ofthe cooling fan 36 over the aluminum sensing ferrule 84. A bore 102through the insulation 20 forms a heatsensing chimney to receive thecollar 88 of the ferrule. The chimney terminates at the oven vent duct98. The heat pickup from the vent duct 98 is determined by the proximityof the ferrule to the duct. It is not affected by the density of theinsulation. The ferrule must be close enough to open switch 82 if thefan fails but not so close as to give false indications of overheatingduring normal cleaning cycles. If fan 36 fails, airflow across thehousing for the thermostatic switch 82 ceases and the switch 82overheats more quickly in response to heat in the chimney and opens oneside of the power supply to deenergize the heating elements 42, M. Onthe other hand if the oven temperature control assembly 46 fails in aheat ON condition, the heat exhausted from the overtemperature ovencavity through the oven vent duct 98 will build up excessivetemperatures in the duct 98. This heat buildup will be sensed by theferrule 84 and conducted to the thermostatic switch 82 which will opento deenergize the heating elements 42, 44. The heat buildup in this caseis sufficient to cause switch 82 to open irrespective of the operationof fan 36.

It should now be seen that an improved protective system has beenprovided wherein a single thermostatic means, because of its particularrelationship to the oven vent and cooling fan, operates to protectagainst overtemperature conditions within the oven.

While the embodiments of the present invention as herein disclosedconstitute preferred form, it is to be understood that other forms mightbe adopted.

lclaim:

1. In an oven comprising an oven liner and a front-opening access doorforming an oven cooking cavity, heating means for cooking food placedwithin the cavity as well as for pyrolytically removing food soil fromthe inner wall surfaces of the oven cavity, oven thermostat meansincluding oven temperature responsive switch means in power supplyrelationship with said heating means for controlling said heating meansbelow a predetermined temperature limit, an oven vent in an upper wallof the oven liner, a catalytic oxidation unit communicating with theoven vent for degrading the hot oven gases before they are returned tothe atmosphere, duct means connected to the oxidation unit fordischarging the degraded hot oven gases to the atmosphere, an inner ovencabinet surrounding the oven liner, insulation between said oven linerand said inner oven cabinet encompassing said duct means, an outer ovencabinet surrounding the inner oven cabinet but spaced therefrom to forman air passageway therebetween, a transverse partition in the airpassageway to form a plenum chamber, fan means mounted through thepartition and adapted to blow cooling air through said air passageway,and an air outlet opening from the plenum chamber, the inventioncomprising an overtemperature protective means protecting againstfailure of said fan means and said oven thermostat means, saidprotective means including a temperature limiting thermostatic switchmeans and a sensing ferrule, said ferrule supporting saidtemperature-limiting thermostatic switch means and extending throughsaid inner oven cabinet and said insulation toward said duct means todefine with said insulation a heat-sensing chimney which conveys heat tosaid ferrule from the degraded hot oven gases in said duct means as ameasure of the temperature of said oven cavity, said temperaturelimitingthermostatic switch means including a single limit switch only in serieselectrical supply relationship with said oven temperature responsiveswitch means and having a first limit switch actuating portion intemperature sensing relation with said ferrule to sense anovertemperature condition in said oven cavity and a second limit switchactuating portion in heat transfer with the cooling air blown by saidfan means to sense a failure condition of said fan means to blow coolingair through said air passageway, thereby to terminate heating in saidoven cavity by interrupting power supply to said heating means uponoccurrence of either of said conditions.

2. The overtemperature protective means of claim 1 wherein the extensionof said ferrule terminates short of said duct means.

3. The over-temperature protective means of claim 1 wherein said firstlimit switch actuating portion nests in chimney-closing relation to saidferrule and said second limit switch actuating portion is supported bysaid ferrule in said air passageway.

4. A built-in wall oven comprising an oven liner and a frontopeningaccess door forming an oven cooking cavity, an oven control panellocated directly above the door, heating means for cooking food placedwithin the cavity as well as for pyrolytically removing food soil fromthe inner wall surfaces of the oven cavity, oven thermostat meansincluding oven temperature responsive switch means in series electricalsupply relationship with said heating means for controlling said heatingmeans below a predetermined temperature limit, an oven vent in the topwall ofthe oven liner, a catalytic oxidation unit communicating with theoven vent for degrading the hot oven gases before they are returned tothe atmosphere, duct means connected to the oxidation unit and directedto the front of the oven for discharging the degraded hot oven gases tothe atmosphere, an inner oven cabinet surrounding the oven liner,insulation between said oven liner and said inner oven cabinetencompassing said duct means, an outer oven cabinet surrounding theinner oven cabinet but spaced therefrom to form an air passagewaytherebetween which also encompasses the control panel, a transversepartition in the air passageway above the oven cavity to form a plenumchamber with the control panel, fan-means mounted through the partition,an air outlet opening from the plenum chamber located above the top edgeof the door adjacent said duct means, and overtemperature protectivemeans protecting against failure of said fan means and said oventhermostat means, said protective means including a temperature-limitingthermostatic switch means and a sensing ferrule, said ferrule supportingsaid temperature-limiting thermostatic switch means and extendingthrough said inner oven cabinet and said insulation toward said ductmeans to define with said insulation a heatsensing chimney which conveysheat to said ferrule from the degraded hot oven gases in said duct meansas a measure of the temperature of said oven cavity, said temperaturelimiting thermostatic switch means including a single limit switch onlyin series electrical supply relationship with said oven temperatureresponsive switch means and having a first limit switch actuatingportion in temperature-sensing relation with said ferrule to sense anovertemperature condition in said oven cavity and a second limit switchactuating portion in said plenum chamber in air-cooled relation to saidfan-means to sense a failure condition of said fan-means to blow airthrough said plenum chamber to said air outlet opening, thereby toterminate heating in said oven cavity by interrupting electrical supplyto said heating means upon occurrence of either of said conditions.

a r w r 4: 5

UNITED STATES PATENT OFFICE Page i of 2 CERTIFICATE OF CORRECTION PatentNo. 3,619,564 Dated November 9, 1971 Inve t x) George W gchager. Jr.

It: is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

FColumn l I line 12, "liquid-filled" should read liquid filled ---7 line19, "185iX 6 F. should read 185 F. i 6 F.

line 24, "overtemperature" should read over-temperature line 43,"heatsensing" should read heat sensing line 54, "HFIG. 2" should readFIGURE 2 Column 2 lines 63,) "overtemperature" should read 64 and 68)over-temperature line 73, "203 iF." should read 203 F. 1 10 F.

Column 3 lines 41) "overtemperature" should read and 1) over-temperatureColumn 4 PO-ww UNITED STATES PATENT OFFICE Page 2 of 2 CERTIFICATE OFCORRECTION Patent No. 3L619, 564 Dated November 9, 1971 Invenron'x)George w. Schauer, Jr.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 4 (Cont'd) line 7, "temperature-limiting" should read temperaturelimiting line 10, "heat-sensing" should read heat sensing line 12,"temperature-" should read temperature lines 17) "overtemperature"should read and 24) over-temperature lines 29) "chimney-closing" shouldread and 30) chimney closing line 54, "fan-means" should read fan meansline 58, "overtemperature" should read over-temperature lines 60)"temperature-limiting" should read and 62) temperature limiting line 64,"heat-" should read heat line 71, "temperature-sensing" should readtemperature sensing line 72, "overtemperature" should readover-temperature lines 74-75, "fan-means" should read fan means dignedand sealed this L th dl lb of July 1972.

(SEAL) v f ttest:

ED.\I.A2.?. I) M FLirlTC H ER, J1 RU BE HT GC TT SC H AL 11 Attontinp;Officer Commissioner of Patents

1. In an oven comprising an oven liner and a front-opening access doorforming an oven cooking cavity, heating means for cooking food placedwithin the cavity as well as for pyrolytically removing food soil fromthe inner wall surfaces of the oven cavity, oven thermostat meansincluding oven temperature responsive switch means in power supplyrelationship with said heating means for controlling said heating meansbelow a predetermined temperature limit, an oven vent in an upper wallof the oven liner, a catalytic oxidation unit communicating with theoven vent for degrading the hot oven gases before they are returned tothe atmosphere, duct means connected to the oxidation unit fordischarging the degraded hot oven gases to the atmosphere, an inner ovencabinet surrounding the oven liner, insulation between said oven linerand said inner oven cabinet encompassing said duct means, an outer ovencabinet surrounding the inner oven cabinet but spaced therefrom to forman air passageway therebetween, a transverse partition in the airpassageway to form a plenum chamber, fan means mounted through thepartition and adapted to blow cooling air through said air passageway,and an air outlet opening from the plenum chamber, the inventioncomprising an overtemperature protective means protecting againstfailure of said fan means and said oven thermostat means, saidprotective means including a temperature limiting thermostatic switchmeans and a sensing ferrule, said ferrule supporting saidtemperature-limiting thermostatic switch means and extending throughsaid inner oven cabinet and said insulation toward said duct means todefine with said insulation a heat-sensing chimney which conveys heat tosaid ferrule from the degraded hot oven gases in said duct means as ameasure of the temperature of said oven cavity, saidtemperature-limiting thermostatic switch means including a single limitswitch only in series electrical supply relationship with said oventemperature responsive switch means and having a first limit switchactuating portion in temperature sensing relation with said ferrule tosense an overtemperature condition in said oven cavity and a secondlimit switch actuating portion in heat transfer with the cooling airblown by said fan means to sense a failure condition of said fan meansto blow cooling air through said air passageway, thereby to terminateheating in said oven cavity by interrupting power supply to said heatingmeans upon occurrence of either of said conditions.
 2. Theovertemperature protective means of claim 1 wherein the extension ofsaid ferrule terminates short of said duct means.
 3. Theover-temperature protective means of claim 1 wherein said first limitswitch actuating portion nests in chimney-closing relation to saidferrule and said second limit switch actuating portion is supported bysaid ferrule in said air passageway.
 4. A built-in wall oven comprisingan oven liner and a front-opening access door forming an oven cookingcavity, an oven control panel located directly above the door, heatingmeans for cooking food placed within the cavity as well as forpyrolytically removing food soil from the inner wall surfaces of theoven cavity, oven thermostat means including oven temperature responsiveswitch means in series electrical supply relationship with said heatingmeans for controlling said heating means below a predeterminedtemperature limit, an oven vent in the top wall of the oven liner, acatalytic oxidation unit communicating with the oven vent for degradingthe hot oven gases before they are returned to the atmosphere, ductmeans connected to the oxidation unit and directed to the front of theoven for dischargiNg the degraded hot oven gases to the atmosphere, aninner oven cabinet surrounding the oven liner, insulation between saidoven liner and said inner oven cabinet encompassing said duct means, anouter oven cabinet surrounding the inner oven cabinet but spacedtherefrom to form an air passageway therebetween which also encompassesthe control panel, a transverse partition in the air passageway abovethe oven cavity to form a plenum chamber with the control panel,fan-means mounted through the partition, an air outlet opening from theplenum chamber located above the top edge of the door adjacent said ductmeans, and overtemperature protective means protecting against failureof said fan means and said oven thermostat means, said protective meansincluding a temperature-limiting thermostatic switch means and a sensingferrule, said ferrule supporting said temperature-limiting thermostaticswitch means and extending through said inner oven cabinet and saidinsulation toward said duct means to define with said insulation aheat-sensing chimney which conveys heat to said ferrule from thedegraded hot oven gases in said duct means as a measure of thetemperature of said oven cavity, said temperature limiting thermostaticswitch means including a single limit switch only in series electricalsupply relationship with said oven temperature responsive switch meansand having a first limit switch actuating portion in temperature-sensingrelation with said ferrule to sense an overtemperature condition in saidoven cavity and a second limit switch actuating portion in said plenumchamber in air-cooled relation to said fan-means to sense a failurecondition of said fan-means to blow air through said plenum chamber tosaid air outlet opening, thereby to terminate heating in said ovencavity by interrupting electrical supply to said heating means uponoccurrence of either of said conditions.